The ultimate goal of this Program is to develop an intravaginal ring (IVR) for sustained delivery of a combination microbicide that will be safe and effective in preventing the sexual transmission of human immunodeficiency virus (HIV) and herpes simplex virus (HSV). A safe and effective microbicide will likely require sustained, local delivery of a combination of antiretroviral drugs that target different steps in the HIV life cycle and a delivery system that overcomes the challenges related to adherence. This will be accomplished through IVR formulation of the reverse transcriptase inhibitor, tenofovir disoproxil fumarate (TDF), combined with the entry inhibitor, maraviroc (MVC). The rationale for pursuing this combination is based on the recent promising results of CAPRISA 004 in which significant protection against HIV-1 and HSV-2 was observed with 1% TFV gel. Ongoing work in Projects 1 and 2 demonstrate potential advantages of a TDF compared to a TFV IVR, including more potent activity against HIV and HSV, greater tissue permeability, and the successful development of a polyurethane (PU) IVR formulation of TDF. An exploratory pre-Phase I study is proposed in this new Project to rigorously measure the pharmacokinetics (PK), pharmacodynamics (PD) and safety of TDF following ring delivery in healthy women. The primary outcomes to be measured are PK of TDF release into the genital tract and adverse events. PD will be evaluated by measuring the antiviral activity (HIV and HSV) in genital tract secretions (luminal) and tissue following IVR delivery of TDF. Ectocervical tissue will be challenged ex vivo with virus to assess drug bioavailability and activity. The impact of PU IVRs on the mucosal immune environment will be assessed by quantifying immune cell populations in the genital tract and concentrations of inflammatory, anti-inflammatory and soluble mucosal immune mediators in genital tract secretions. Advanced molecular microbiological tools will be employed including broad range 16S rRNA gene PCR with pyrosequencing to define the bacterial communities, and fluorescence in situ hybridization to determine if rings alter the epithelium and lead to vaginal biofilm formation. Results will inform the design of a Phase I trial of a TDF-MVC combination IVR.